KevinL
Flashlight Enthusiast
I just wrote this up in a PM to help a fellow member and decided to share the knowledge with others as well.
Posted here as it was too specific for the Cafe and too general for flashlight discussion (because it really is about camera talk and how we use them to achieve a particular purpose with lights!)
Posted here as it was too specific for the Cafe and too general for flashlight discussion (because it really is about camera talk and how we use them to achieve a particular purpose with lights!)
KevinL said:*edited for general posting*
Contrary to popular belief you do not need a tremendously high powered camera to take beamshots. My little Canon A530 compact point and shoot does the job (almost) as well as my big Canons. I use the big ones because they're the ones I use most of the time
There are two kinds of beamshot I take - the first is the 'relative' beamshot. This beamshot needs two (or more) lights, both in the same picture, and I generally use an automatic mode for them like P (Program AE) with the flash disabled. No fancy stuff there, P just gets the camera to set automatic metering and turn off the flash.
This beamshot is always an accurate comparison of both lights, but only in the same photo. Auto settings are fine. The problem with this beamshot is that you cannot compare two different photos.
For the different photos you must lock your parameters. ANY parameters will do (within reason) as long as they are consistent. I'll give you a brief outline plus explain the rationale behind manual settings.
The whole idea behind manual settings of a camera is how much light reaches either the film or digital image sensor (I'll just call either of these the imager). You have three essential controls in manual mode, shutter speed, aperture, and ISO. The whole tricky bit is to balance all three settings to achieve the 'appropriate' amount of light falling on the imager. Kinda like balancing your clutch, throttle, and gearbox to achieve your desired speed in a car. Just like cars, automatics are available.. in which the camera can set one or more of the above according to its logic.
Shutter speed is how long the imager is exposed to light. Measured in seconds, usually fraction of a second, say 1/60. If you do the maths dividing 1 by 60, it gives you a value in seconds as to how long the shutter is open. Cameras also allow you to go into seconds and we just write "1 second", "15 seconds" or something like that. Those are very long exposures, a tripod is recommended to prevent the image from being blurred as nobody can hold perfectly still for that long.
Therefore 1/20 is 0.05 sec, 1/60 is 0.0167 rounded up, and 1/250 is 0.004. It becomes easier to see how a shutter open for a shorter time gathers less light, and what the values actually mean.
Aperture is a tricker concept. It involves placing an aperture in front of the lens to restrict the amount of light passing through it and falling onto the imager. An analogy would be like cupping your hand around a flashlight's bezel. As you tighten your fist (closing the aperture) less light escapes out of the front. As you loosen up your hand more light gets out. Aperture is usually written as f/ followed by a number ie. f/2.8.
Alternatively you could try placing a piece of paper in front of a light (that is not likely to set the paper on fire. Do not attempt with USL or similar super-incans). Poke a small hole (small aperture) in the paper, a little bit of light gets out. Widen the hole (open up the aperture) - more light gets out. Like shutter speed, aperture is represented as a fraction, hence f/1.4 (f "divided" by 1.4) would be a very big aperture with a large opening, vs f/8, which would be a very small aperture (f "divided" by 8). Just to help you conceptualize it, you may think of "f" as the number "1", hence 1/1.4 is greater than 1/8. (this of course ignores the technicalities of what f really represents from a mathematical perspective...but we won't go there)
ISO is simply sensitivity - how 'sensitive' the imager is to light falling on it. Again the more sensitivity the less light you need to create a viable image. ISO is usually followed by a number, ISO 100, ISO 200, etc. Of course turning up the sensitivity (like an amplifier - in fact, signal amps are used for this purpose in digital cameras) also amplifies any noise present in the input and this appears as 'grain' or blotches of color in your image. The holy grail would be to find a noise reduction system that strips away all noise leaving a perfect signal. If you can make one, you could put Canon, Nikon, and everybody else out of business overnight.....or have all of them as your customer
A large part of the technical expertise in photography revolves around figuring out what combination of these will achieve the effect you want. This part would take years to learn and I'll simplify it by giving you a set of 'recommended' settings. I would use 1/60 shutter speed, f/4, ISO 100 for small lights and keep the camera close to the light source (inverse square law, light falls off as you get further from it!). Say about 3ft. These settings are reasonable for most cameras and almost all of them should be able to do it.
For very high powered incandescent lights this may result in overexposure or 'blowouts' where the whole image goes white due to too much light. So I would vary the shutter speed to 1/250, but keep all the rest of the settings the same (f/4, ISO 100). Now the shutter opens and snaps shut for a much smaller fraction of time, preventing overexposure. This can be your 'high powered light' setting. Use the previous setting for general purpose lights.
Also, the beauty of all of this is that if you list your settings, and your distance to the wall (important that distance be kept consistent), someone else can replicate your settings in the comfort of their own home.
Also, one more useful setting that is optional - white balance. If you want to be even more consistent in the tint of the lights from image to image, lock your camera on Daylight white balance instead of Auto. If you don't, it is no big loss (I don't always bother), but if you do it improves 'tint' consistency.
Hope this helps!
